Biology Unit 1 AS level (AQA)

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Biology Unit 1
Pathogens, Lifestyle and Disease
Disease: the malfunction of part, or whole, of the body with a characteristic set of symptoms
Pathogen: an organism, usually a microorganism, which causes disease
Causes of disease:
Infections ­ caused by pathogens
Non-infectious ­ resulting from your genetics and/or the environment (includes
Three major types of pathogen:
1. Bacteria (single celled prokaryotic cells)
2. Viruses (consist of protein coat and nucleic acid)
3. Fungi (eukaryotic organisms which could be single celled or filamentous)
Routes of infection:
Breaks in the skin
Reproductive/urinary system
Lining of the digestive system
Gas exchange system
Once the pathogens infect the body, they cause disease because:
1. Cause direct damage to the body cell
2. Release toxins which damage body cells
Risk Factors: factors that increase your chance of developing a disease
A mutation within the DNA may cause the body cells to divide uncontrollably resulting
in a tumour.
Risk factors:
o Exposure to ionising radiation
o Exposure to carcinogenic chemicals
o UV rays (sun/sunbeds)
o X-rays
Inherited genes can make some people more susceptible than others (e.g.; breast
Coronary Heart Disease (CHD)
This is covered in the heart and heart disease topic

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Data Handling
REMEMBER THIS: %change = change x 100
Common question:
1. `Explain the advantage of giving these data as percentages.' 2 marks
Easier to compare if the sample size effectively the same
Different numbers of people in each group
Correlation: shows that there is a relationship between two variables; however, it might not be a
causal one.…read more

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Site of ATP production from aerobic respiration
Bound by double membrane
o Inner membrane = cristae
Functions to increase SA for attachment of enzymes in respiration
o Within the inner = matrix
Contains proteins, lipids and some DNA
Endoplasmic Reticulum (ER)
Continuous with the nuclear membrane
Forms series of enclosed flattened sacs called cisternae
ER provides large SA for chemical reactions
Provides a pathway for the transport of materials throughout
the cell
Rough Endoplasmic Reticulum (RER)
Transports proteins throughout the cell
Have ribosomes on its…read more

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Known as a fluid mosaic model
All cell membranes have the same basic structure, but different proportions of molecules
relating to it's function
Finger like projections
Increase the surface area of the cell membrane
Function in cell division to form a network of spindle fibres
These fibres pull the chromosomes apart
Bacterial Cell
Prokaryotic: `before nucleus', they do not have a nucleus or other membrane bound organelles.…read more

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Specimens Living Dead
Cost Low High
Image Colour Black and white ONLY
Wavelength Long Short
Shorter the wavelength, the better the resolution!
Two types of electron microscopes:
Transmission Electron Microscope (TEM)
o Transmits electrons through thin specimen
o Most common form of microscope
o Best resolution
o Produces 2D images
Scanning Electron Microscope (SEM)
o Scans a fine beam of electrons onto a specimen
o Poorer resultion
o Excellent 3D image
o Samples do not have to be thin
REMEMBER THIS: Original Size = Image…read more

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Specific phagocytosis
A specific response to a specific antigen on the surface of a cell or pathogen that has
been recognised as non-self
Antigen: a molecule (usually protein) that stimulates an immune response resulting in the production
of specific antibodies
The surfaces of all cells are covered in antigens; they act as markers that help identify each particular
type of cell to the host organism. Therefore, if antigens aren't recognised an immune response will
be initiated.…read more

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Passive: antibodies are received from elsewhere ­ can be given by a mother or an antiserum
(injection of antibodies)
Active: provided by the memory cells that are produced after a primary immune response to a
Vaccines consist of either dead, weakened or attenuated (low virulence) specific pathogens. The
vaccine will initiate an immune response in the individual, producing memory cells, but without the
symptoms associated with a full infection.…read more

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Mice are genetically engineered to produce human antibodies
Few cases of human volunteers suffering major and unexpected side effects when testing
the monoclonal antibody
Amino Acids and Proteins
Monomers and Polymers
Monomers: small identical or similar molecules
Polymers: large molecules made from joining many identical or similar monomers together
Monomers are joined together by condensation reactions ­ this involves the removal of one H2O
molecule.…read more

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Number of peptide bonds will always be one less than the number of amino acids
joined together
Protein Structure
Number and sequence of amino acids (polypeptide chain) which is dictated by
your DNA
Proteins differ from each other because their primary structures are different
Hydrogen bonds (weak) form and fold the chain into an alpha helix and a beta
Further folding of the polypeptide chain into a specific complex 3D shape
R groups form bonds between them
Ionic bonds between oppositely…read more

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Enzymes: biological catalysts ­ increase the rate of chemical reaction but remain unchanged by the
Enzymes lower the activation energy needed for chemical reaction
Activation Energy: minimum energy required for a successful chemical
reaction to take place
Enzymes are proteins that have specific complimentary active sites to
their substrate. This allows enzyme-substrate complexes to be formed.…read more



Really great notes! I don't suppose you have any for Unit 2?


Really great notes! I don't suppose you have any for Unit 2?

Scarlett Tankard

Thanks! I've not completed my unit2 ones yet, but when I do, I'll be sure to upload them!


AMAZING thanks so much !!


thank you!! could you post unit 2 please?

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